Method of making insulated  tubes



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J/A/ M *Af/y F. F. LUCAS METHOD OF MAKING INSULATED TUBES Filed ADril 27.

Nov., il B924,

IIIIIIIIIIUI!lllllllllllllfllllllllf Patented Nov. l1, 1924.

UNITED STATES PATENT' OFFICE.

CIS F. LUCAS, OF EAST ORANGE, NEW JERSEY, SSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OIE' NEW YORK, N. Y., A CORPORATION OF NEW YORK.

METHOD OF MAKING INSULATED. TUBES.

Application led April 27, 1920. Serial No. 376,966.

To aZZ whom it may concern:

Be it known that I, FRANCIS LUCAS, a citizen of the United States, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful improvements in Methods of Making Insulated Tubes, of which the following is a full, clear, concise, and exact description.

lThis invention relates to a process of constructing electrically insulated tubes.

It has been considered desirable in the past to employ fiber tubing in electrical apparatus as a protective covering for electrical contacts and connections. Its use, however, has met with serious objections due to the fact that the traces of zinc salt remaining in the fiber from the manufacturing processes employed, cause corrosion of the metallic parts adjacent thereto. This is especially true when such tubing is used in humid atmospheres. The corrosion which takes place is not only due to chemical action of the occluded salts but also to electro-chemical action produced either by local action of a galvanic couple or by the difference in potential maintained by the applied electro-motive force. onsiderable attention has been given to this diiiiculty, but no satisfactory means of preventing deleterious `effects of the occluded salts have been found. The withdrawal of all the moisture and the covering of the fiber with a suitable protective composition does not accomplish the desired result. Such a process renders the ber extremely brittle and, therefore, unable to stand up under the usual conditions of operation.

It is an object of this invention to produce a satisfactory tubular insulating medium which will be free from the objections pointed out above. p

Another object of this invention is to develon a method by which such an insulated tubing may be constructed.

It has been found that a metal tube insulated on its inner and outer surfaces produces a satisfactory tubular insulating medium and one which is free from the objections pointed out above. As a covering for the metal tube, impregnated fibrous material, such as paper, cloth and the like, is well suited for use. Natural or synthetic resinous material is employed as the basis of the impregnating compound in the preferred form of the invention. Phenolic condensation nroducts, such as bakelite, redmanol and con method by which these insulating layers are applied may be more readily understood by reference to the drawings accompanying the specification.

Fig. l shows a separable mandrel wound with insulating paper; Fig. 2 represents the metallic tube slipped over the paper covering the mandrel and wound with insulating paper; Fig. 3 represents the assembled unit in a pressure device; Fig. 4; shows an end view ofthe assembled unit; Fig. 5, illustrates the curing process; Fig. 6 is a view of the finished article, and Fig. 7 shows one application of a metal tube insulated according to this invention.

Referring now to Fig. l, the separable mandrel l, constructed preferably of steel, is assembled and held together by the knurled collar 2. Paper 3, which has been impregnated with a phenol lastic is then wound on the mandrel until tlie desired thickness of insulation is obtained. The tube which is to constitute the basis of the iinished product, is then slipped over the paper-wrapped mandrel, the tube being shown by' 4 in Fig. l2. Preferably the ends of the metal tube are rounded ofi' andits surface roughened by subjecting it to a sand blast. The width of the paper wound on the mandrel must be so taken that it will extend beyond the two ends of the metal tube when the latter is in the required position. Over the metal tube other layers of the impregnated paper 5 are placed. This wrapping is also slightly longer than the metal tube so as to allow for folding over at each end. The structure thus obtalned is then placed in a mold 6, as shown in Fig. 3, which is especially designed so that it exactly conforms to the desired shape and size of the inal product. Bevels are provided at each end of the molding chamber proper, the function of which is to form the impregnated paper over the ends of the metal tube. The iron frame clamp 7 is slipped over the mold and the bolt 8 tightened. The key 9 is then inserted inthe mandrel. Fig. 4, which is an end view of the assembled unit,

show-s` clearly the structure as it has been thus built'up. In Fig. 4, 1 shows the mandrel 3 the first Wrapping 0f impregnated paper, 4 the metal tube, 5 the second Wrapping of the paper, and 9 the inserted key. The key v is then turned, thus forcing thelwrapping adjacent the mandrel against the inner surface of the metal tube. This is shovvn in Fig. 5. In order to cure the impregnated medium and to secure the material firmly tothe metal tube, the complete structure is subjected to a definite heat. In Fig. 5 the heating means shown consists of an electrically heated oven. After the baking has been continuedA for a sufficient length 0f time, the mold is removed and cooled. The finished product thus obtained being shown in Fig. 6. Fig. 7 shows the application of the metallic tube insulated in the manner described above -to a telephone plug, the function of such covering being to protect the electrical contacts and connections contained therein.

While particular apparatus has been described herein for use in carrying out this invention, it is probable that in manufacturing such insulated tubes on a large commercial scale, modifications would be made in order that the operations might be carried out in the most efficient manner. For example, instead of the separable mandrel which is employed according to the specification, any other expansion means might be used, such as forcing compressed air inside an impregnated tube. The pressure apparatus could Well be embodied in the oven structure substantially as shown in Fig. 5, except that the clamping device would be extended through the body of the oven so that it could be operated from the outside, so that no heat would be lost in removing the iron frame from the oven each time. When the impregnating medium consists of adhesives or glutinous materials, the curing operation `may be dispensed with. Other changes may thus be made Without departing from the spirit of the invention.

Thus a means is provided whereby the mechanical shocks and'abrasion due to the handling of telephone plugs and like'apparatus, are prevented from causing injury to the electrical conductors within. Moreover, the structure as developed according to the process set forth herein is entirely noncorrosive and at the same ,time affords a completely insulated handle, thus preventing any possible short circuiting. Tests made With a telephone plug utilizing the insulated shell as made according to the process described, have shovvnfthat it is far superior to the liber shell heretofore employed. Although its use in connection with telephone apparatus has been more specifically referred to, this insulated metal tube may also be utilized toIadvantage Wherever its particular properties are adapted for such use.

What is claimed is:

1. The method of electrically insulating a metallic tube which consists in Wrapping impregnated sheets of fibrous material about an expansion device, slipping the metallic tube over the same and forcing the impregnated fabric against the sides of the tube by means of pressure applied thereto through the medium of the expansion device.

2. The method 0f electrically insulating a metallic tube. which consists in Wrapping impregnated fabric about an expansion device, slipping the metallic tube over the same, Wrapping the latter with impregnated fabric, placing the structure so obtained in a mold and expanding said expansion device, and compressing the mold thereby forcing the impregnated fabric into contact with the tube. i

3. The method of electrically insulating a metallic tube which consists in wrapping impregnated fabric about an expansion device, slipping the metallic tube over the same, placing the structure so obtained in a mold, expanding said expansion device to force the fabric into contact with the tube and curing the impregnating medium. y

4. The method of electrically insulating a metallic tube which consists in Wrapping impregnated fabric about an expansion device, slipping the metallic tube over the same, Wrapping the latter with impregnated fabric, placing the structure so obtained in a mold expanding said expansion device to force the fabric into contact with the tube and curing the impregnating medium.

5. The method of electrically insulating the inner surface`of a metallic tube which comprises Wrapping about an expansion device sheets of fibro'us material impregnated with a phenolic condensation product, slipping theI metallic tube over the same, expandng said expansion device so as to force the impregnated'fabric against the tube and heating While the insulation is under pressure so as to cure the phenolic condensation product.

In witness whereof, I hereunto subscribe my name this 24th day of April A. D., 1920.

FRANCIS F. LUCAS. 

